The present invention is related to the field of routed networks, and more particularly to routed networks employing virtual private routed network (VPRN) techniques.
One of the challenges facing designers of data communications networks is to provide improved performance in the face of tremendous growth in network size and complexity. As the number of nodes using distinct network addresses in a network grows, the sizes of routing tables used for routing in the network increase, and more processing power is required to calculate routes and carry out the routing of network traffic. In fact, the processing load associated with routing increases generally as the square of the number of distinct routes. In large networks having a generally flat shared address space, such as the Internet, it may be infeasible for routers to support sufficiently large routing tables, due to constraints in the available processing power.
It has been known to emulate a private, wide-area routed network within another, generally more public, wide-area network. Such an emulated network is referred to as a virtual private routed network (VPRN). Because a VPRN “piggybacks” on a separate and generally shared network, it can be more cost effective than a distinct private wide area network. At the same time, there is significant functional separation between the VPRN and the underlying network, so that VPRN largely behaves like a standalone network, with attendant benefits in security, network management, and other aspects of network operation.
In a common VPRN configuration, the VPRN employs Internet Protocol (IP) technology of the same type used in the Internet, complete with a private instance of a distributed IP routing protocol such as Open Shortest Path First (OSPF) and a private set of network addresses such as IPv4 addresses. A mesh of “tunnels”, or dedicated virtual channels, are established among a set of router nodes in the Internet. The router nodes encapsulate VPRN traffic in a format required by the tunnels, transmit encapsulated traffic to other router nodes using the Internet address space and routing protocols, decapsulate received traffic to recover the original VPRN traffic, and then use the VPRN routing protocols and address space to forward the traffic to other nodes in the VPRN outside the Internet.